Reduction of inhibitory signaling and selective induction of C-C motif chemokine ligands after spinal cord ischemia

We used our mouse model of transient aortic cross clamping (ACC)-induced ischemic spinal cord injury (ISCI) to identify the early molecular changes in the spinal cord (SC) after ACC that contribute to delayed paraplegia in 65-70% of mice. SCs were collected one and four hours (h) after ACC, segmented into cervical and thoracic+lumbar (Th-Lu) sections, and RNA was sequenced. The non-ischemic cervical SC was used as control for the 1h post-ACC mice. At 4h, the transcriptome of ACC Th-Lu sections was compared with the transcriptome of sham Th-Lu. The Th-Lu SCs of sham and ACC mice at 4h post–surgery underwent LC-MS/MS phospho-proteomic analysis to identify differentially phosphorylated proteins.At 1h after ACC, transcripts involved in the mitochondrial respirasome electron transport chain (ETC) were downregulated in the ischemic Th-Lu region of the SC. This reduction was paralleled by the induction of pro-inflammatory chemokines Ccl2, Ccl3, and Ccl4, which were further amplified at 4h but only in ~two-thirds of mice. The later increase was paralleled by the downregulation of transcripts encoding post-synaptic membrane proteins, particularly of the GABAergic synapse. Proteins involved in post-synaptic density and synaptic plasticity were found to be hypo-phosphorylated following ISCI. Our data shows that ISCI reduces transcripts for ETC proteins likely leading to a lack of stability in the GABAergic post-synaptic organization and function at 4h. Thus, pharmaceuticals aimed at stabilizing inhibitory synapses may be more effective than excitatory receptor antagonists for alleviating excitotoxicity. On the other hand, the selective induction of Ccl chemokines in a 2:1 ratio of ACC mice (similar to the rate of paralysis at 48h) suggests tight association between intraspinal Ccl induction and paralysis. We posit that combining antagonists for Ccls and/or their receptors with pharmaceuticals aimed at stabilizing GABAergic synapses will be a potent neuroprotective drug regimen after aortic surgery.